Generally, when manufacturing semiconductor integrated circuits, it is necessary to conduct etching on an interlayer insulating film formed on a silicon wafer. A plasma etching device is used in order to conduct etching on this silicon wafer having the interlayer insulating film (hereinafter referred to as a wafer), and silicon is used as the electrode material inside this device. As shown in the schematic explanatory view of a partial cross-section in FIG. 1, the silicon electrode plate for plasma etching has a structure provided with etching gas ejecting through-holes 5 arranged in parallel in the thickness direction of the silicon single crystal plate. This silicon electrode plate for plasma etching 1 is fixed approximately at the center inside a vacuum container (not illustrated). A wafer 4 is placed on a stand 6, and high frequency voltage is impressed while etching gas 7 flows toward the wafer 4 through the etching gas ejecting through-holes 5. Thereby, plasma 2 is generated between the silicon electrode plate for plasma etching 1 and the wafer 4, and this plasma is made to act upon the wafer 4 to etch the surface of the wafer 4.
When plasma etching is conducted using a silicon electrode plate for plasma etching 1, electrical charge concentration areas (edge portion on which electrical charge is concentrated) are generated locally at the terminal openings of the etching gas ejecting through-holes 5 that contact the plasma 2, and these portions are more subject to wear. With respect to the etching gas ejecting through-holes 5 which are provided parallel to the thickness direction of the silicon electrode plate for plasma etching 1, as shown in FIG. 2, the opening of the etching gas ejecting through-holes 5 that contacts the plasma 2 becomes enlarged as it wears away so that it widens toward the bottom. Thereby, abrasion holes 3 are formed.
In the conventional silicon electrode plates for plasma etching 1 which are composed of silicon single crystal plates, the abrasion holes 3 are easy to be generated, and the length α in which the etching gas ejecting through-holes 5 has uniform diameter is reduced due to the formation of the abrasion holes 3 by plasma etching operations. Thereby, the wafer etching tends to become irregular.
In order to solve the above problem, a silicon electrode plate for plasma etching has been offered that is made of silicon containing 0.01 ppm to 5 mass % of a dopant of any one element selected from among P, As, Sb and B. This silicon electrode plate for plasma etching composed of the doped silicon single crystal plate has superior electrical conductivity; thereby, the formation of abrasion holes 3 due to generation of localized electrical charge concentration areas is suppressed. Accordingly, it is said that abrasion of the etching gas ejecting through-holes 5 is reduced, the flow of etching gas becomes uniform, and the lifetime is extended (see Patent Document 1 or 2).
However, it is impossible to avoid generation of the above-described abrasion holes 3 due to the plasma etching over a long period of time. Moreover, since in-plane irregularities occur with respect to the generated amount of the abrasion holes 3 formed in the silicon electrode plate for plasma etching 1, with the growing demands in recent years to keep the density of the plasma 2 uniform and maintain a more uniform etching of the wafer 4, the time of use of one silicon electrode plate for plasma etching 1 must be kept short, and early replacement must be conducted. The replaced silicon electrode plates for plasma etching 1 are then scrapped, resulting in a wasteful mode of use.
(Patent Document 1) Japanese Patent Application, First Publication No. H8-37179
(Patent Document 2) Japanese Patent Application, First Publication No. H10-17393